American car used by presiding officer wouldn't be the fastest mode of transport (5,5)
I believe the answer is:
sedan chair
'mode of transport' is the definition.
(I know that sedan chair is a mode of transport)
'american car used by presiding officer' is the wordplay.
'american car' becomes 'sedan' (I've seen this before).
'used by' means one lot of letters go next to another.
'presiding officer' becomes 'chair' (chair is a kind of presiding officer).
'sedan'+'chair'='SEDAN-CHAIR'
'wouldn't be the fastest' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for sedan chair that I've seen before include "Litter" , "Vintage form of transport" , "single-seater vehicle" , "A carrier employing Poles" , "seat" .)